Just go to the source ports section linked on the main page and check them out. You should already be familiar with the more popular ones as they are mentioned all the time (zdoom, jdoom, legacy, prboom, eternity, edge, and boom.)

hey thanks alot what would you recommend i here alto of talk about the boom thing would that be good enough?

Any source port will do (except the dreaded doom95), but the most popular ones are Boom (320x200 only, best for <233 MHz PCs) prBoom, Legacy and ZDoom (all support higher resolutions). There are others of course, see the source ports section of this site for more info.

edit: or see the above posts as well, as they got there while I was typing this one out...

It happens because there are too many sidedefs in view or something similar. It used to be the bane of everyone who tried to make large detailed levels.

Actually its the number of distinct flat areas the game attempts to draw. This has nothing to do with lines, and does not necessarily correspond 1:1 with sectors.

The game merges like flat areas where possible so that it draws the entire area in one pass. For a region to be merged with another visplane, it must: be at the same z level, have the same light level, have the same flat, and contact the region.

Thus if you have 20 sectors with identical attributes, there may only be one visplane for all of them.

If you make a checkerboard map with only 2 different flats, it may have 256 visplanes.

The visplane limit in the original DOOM engine was 128. Lee Killough, who during his time in the community devoted a large amount of time to studying and understanding the visplane behavior (he fully understood it even before the source release!), states in the source that there was no logical reason for this limit.

The source contained a comment trying to justify it in terms of the time needed to generate them or something, but with just a few small and pretty obvious tweaks Lee was able to make that irrelevant.

Thus pretty much all modern ports remove the visplane limit. I think there's a few that might still have it. Legacy at one point had doubled it to 256, but they may have removed it since then. I believe Raven may have increased the limits in Heretic and Hexen, but I don't know for sure.

While I'm lecturing, I'll mention a neat little toy that Eternity contains. If you set the r_showvpo console variable to on, when Eternity detects the approximate number of visplanes that would have overflowed in DOOM, it shows a VPO graphic. Note its only approximate though, because Lee also tweaked BOOM's visplane generation so that more planes are merged (making it much more efficient). So Eternity uses fewer visplanes than DOOM did for the exact same scene in some circumstances. To help make up for this, Eternity adds a small constant number of visplanes to the actual total, and thus is not exact :P Go try it out sometime.